"When I was born, no one had ever been in space. It wasn't hard to fly in space when I was born - it was impossible," he tells The Guide.

Col Hadfield was first inspired to think about space travel when reading science fiction comics and novels as a boy, and watching films and TV shows.

"And then the race to the moon. I turned 10 the summer that the first two people walked on the moon and that was as pivotal as anything," he says.

"The fact that this really happens now, this isn't just a childhood craziness but this is an actual fact, something that other people do, that's really what inspired me and made me want to explore it myself."

Col Hadfield has since been on three space missions, and on his last voyage became the first Canadian to command a spaceship on board the International Space Station.

He was also the first person to record a music video in space, and he is perhaps best known for his rendition of David Bowie's Space Oddity, filmed while floating through the spaceship in 2013.

Col Hadfield says the film clip helped him share his experience in space with more people, something he believes is a "fundamental responsibility and obligation of the job" as an astronaut.

Who knows, he might inspire someone who goes on to discover life in outer space, something he says could be achievable within the next generation.

"I think it's important if you're a young person now dreaming of what it is you want to do in the future, to recognise that impossible things happen as the result of an outlandish science fiction kind of vision of the future and an enormous amount of personal and cooperative, collective work," Col Hadfield says.

The retired astronaut shares his passion for space exploration on The Truth is in the Stars, a documentary led by Star Trek's original Captain Kirk, William Shatner, which looks at how the show influenced popular culture and human innovation.

Canadian astronaut Chris Hadfield in a scene from the documentary The Truth is in the Stars.Max Rosenstein

"Star Trek was very important to me as a kid, as an embodiment of an idea of a future that might well be," Col Hadfield says.

"We're not that far away from a lot of the things that Star Trek imagined, and I think people need to see the link between fantasy and reality and that it's our own creativity that allows the two to marry up."

The Truth is in the Stars airs on Sunday at 7.30pm Qld, 8.30pm NSW on Discovery Science.